1. Field of the Invention
This invention relates to a mold to manufacture an improved bottle cap and, in particular, to a mold with a cavity which is split only in the plane of the cap and not in an axial plane.
2. Brief Statement of the Prior Art
Plastic caps for narrow-necked bottles and containers such as the ubiquitous dairy plastic container are typically of press-on or screw type. The press-on caps used heretofore have an inner or corking skirt dependent from the underside of the top disc of the cap. This corking skirt is received within the neck of the container and the cap is secured about the neck which is thus received between its inner, corking skirt and the outer capping skirt. The outer skirt commonly bears two annular ribs or beads about its inner periphery, axially positioned to be received in annular grooves in the neck finish of the container, and has two parallel score lines between the two annular beads to form a tear band. The tear band construction and upper and lower annular beads has been claimed by its manufacturers as "tamper-proof". The tamper-proof objective, however, has not been achieved. Most press-on caps can be removed without removing the tear bands, with varying difficulty, depending on the design. This shortcoming is inherent in their design, since the caps must be sufficiently elastic to stretch and permit the annular beads to seat in the annular grooves of the bottle neck during the capping operation. A simple application of a sufficient unseating force will remove the entire cap, which when reseated, offers no clue that the container was previously opened.
Recent events in the pharmaceutical industry have underscored the necessity for more secure closures, i.e., for a truly tamper-proof closure, which can also be applied to the dairy, drink and food industries.
Another difficulty commonly experienced with the press-on caps is the lack of precise tolerance in the manufacture of the caps and/or the neck finish of the plastic container. The plastic containers are blow-molded and the neck finish is achieved with dies commonly referred to as shear steel and neck rings. With frequent or prolonged use, the close tolerances of these dies can be lost with the result that the thicknesses of the neck walls can vary significantly from the original specifications. Furthermore, lack of precise control in manufacturing of the caps frequently results in caps in which the tolerances are not carefully controlled. Difficulties are experienced in the capping operations from both of these causes, and are aggravated by the trend to very light-weight plastic dairy containers, such as the 50-gram gallon container. To illustrate, flashing is trimmed from the neck of the containers during their manufacture and, sometimes, this trimming is imperfect so that necks are obtained which are not perfectly in round or in which the flashing is not completely removed. The result of these fabrication errors is that the container neck frequently wedges between the inner and outer skirts of the cap, lifting the cap or preventing the cap from securely seating.
Another difficulty which is experienced with the center corking skirt of the conventional press-on cap is that the lack of flexibility of the corking skirt prevents its use for capping of glass bottles which lack precise tolerances in neck thicknesses.
While the center, corking skirt was envisioned as sealing the caps on the containers such as blow-molded dairy containers and the like, in practice, little or no sealing is actually effected by this corking skirt. Furthermore, the edge of the container that bears against the corking skirt is very narrow and no significant sealing surface is presented, even under ideal manufacturing conditions. In practice, the variations in tolerances of the cap and/or molded plastic bottle prevent even minimal sealing between these members. As a result, the sought-after sealing of caps in containers such as plastic dairy bottles has not been achieved with press-on caps.
Manufacturers of press-on caps have also avoided split cavity molds, i.e., molds which split along axially to the plane of the cap, because of their greater complexity and cost. Consequently, the tab on the tear band of the cap of one manufacturer is formed on the lower edge of the cap skirts, resulting in a spiral tear band, as in U.S. Pat. No. 3,338,446. Caps of this design, however, are prone to split during the capping operation. Other manufacturers have avoided the splitting problem with entirely annular tear bands having lateral tear tabs however, this cap does not have an annular lip on its reclosure cap, and for this reason is inconvenient to the consumer. In my prior patents, U.S. Pat. No. 4,032,029, I disclosed a cap with an annular tear band and tab, and an annular lip. While this cap was a substantial improvement over the aforementioned caps, its manufacturing required the use of a split cavity mold, and it also utilized the less than ideal center corking skirt.